Anti-coalescing agent for three-dimensional printing

ABSTRACT

An example of an anti-coalescing agent for a three-dimensional (3D) printing process includes a vehicle and an anti-coalescing polymer dispersed in the vehicle. The vehicle includes a co-solvent, a surfactant, a humectant, and water. The anti-coalescing polymer has a mean particle size ranging from about 50 nm to about 195 nm, and the anti-coalescing polymer is to coat polymeric build material particles to prevent the polymeric build material particles from coalescing during electromagnetic radiation exposure of the 3D printing process.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process usedto make three-dimensional solid parts from a digital model. 3D printingis often used in rapid product prototyping, mold generation, mold mastergeneration, and short run manufacturing. Some 3D printing techniques areconsidered additive processes because they involve the application ofsuccessive layers of material (which, in some examples, may includebuild material, binder and/or other printing liquid(s), or combinationsthereof). This is unlike traditional machining processes, which oftenrely upon the removal of material to create the final part. Some 3Dprinting methods use chemical binders or adhesives to bind buildmaterials together. Other 3D printing methods involve at least partialcuring, thermal merging/fusing, melting, sintering, etc. of the buildmaterial, and the mechanism for material coalescence may depend upon thetype of build material used. For some materials, at least partialmelting may be accomplished using heat-assisted extrusion, and for someother materials (e.g., polymerizable materials), curing or fusing may beaccomplished using, for example, ultra-violet light or infrared light.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a flow diagram illustrating an example of a method for 3Dprinting disclosed herein;

FIGS. 2A through 2E are schematic and partially cross-sectional cutawayviews depicting the formation of a final 3D object using an example of amethod for 3D printing disclosed herein;

FIG. 3 is a top, schematic view of the build material, with some of thebuild material negatively patterned, some other of the build materialpatterned with a fusing agent, and still some other of the buildmaterial having a detailing agent applied thereon;

FIG. 4 is a schematic and partially cross-sectional view of an exampleof a 3D printing system disclosed herein;

FIGS. 5A through 5D are magnified images, at 100 times magnification, ofan example removable build material portion and a comparative portionbefore and after heating; and

FIGS. 6A and 6B are black and white photos of an example 3D object and acomparative 3D object.

DETAILED DESCRIPTION

Some examples of three-dimensional (3D) printing may utilize a fusingagent to pattern polymeric build material or polymeric composite buildmaterial. In these examples, an entire layer of the polymeric orpolymeric composite build material is exposed to radiation, but thepatterned region (which, in some instances, is less than the entirelayer) of the polymeric or polymeric composite build material is fusedand hardened to become a layer of a 3D object. In the patterned region,the fusing agent is capable of at least partially penetrating into voidsbetween the polymeric or polymeric composite build material particles,and is also capable of spreading onto the exterior surface of thepolymeric or polymeric composite build material particles. This fusingagent is capable of absorbing radiation and converting the absorbedradiation to thermal energy, which in turn fuses the polymeric orpolymeric composite build material that is in contact with the fusingagent.

Other examples of 3D printing may utilize selective laser sintering(SLS) or selective laser melting (SLM). During selective laser sinteringor melting, a laser beam is aimed at a selected region (generally lessthan the entire layer) of a layer of the polymeric or polymericcomposite build material. Heat from the laser beam causes the polymericor polymeric composite build material under the laser beam to fuse.

Fusing (through the use of the fusing agent or the laser beam) causesthe polymeric or polymeric composite build material to join or blend toform a single entity (i.e., the layer of the 3D object). Fusing mayinvolve at least partial thermal merging, melting, binding, and/or someother mechanism that coalesces the polymeric or polymeric compositebuild material to form the layer of the 3D object.

In some instances, the thermal energy converted from the absorbedradiation or applied by the laser beam may bleed or transfer intopolymeric or polymeric composite build material particles that are notin contact with the fusing agent or the laser beam. This bleed ortransfer of thermal energy may result in the polymeric or polymericcomposite build material particles that were not intended to fuse (i.e.,that were not patterned with the fusing agent or did not have the laserbeam applied thereto) fusing or semi-fusing to the 3D object's surface.These fused or semi-fused particles attached to the 3D object's surfacemay reduce the surface finish quality and accuracy of the 3D object. Forexample, the surface may be undesirably rough and/or may have anundesirable appearance. As another example, the 3D object may be largerthan intended.

Disclosed herein is an anti-coalescing agent including a vehicle and ananti-coalescing polymer dispersed in the vehicle. The anti-coalescingagent may be used to negatively pattern portions of the polymeric orpolymeric composite build material (referred to herein as buildmaterial) that are not to become part of the final 3D object but thatmay be exposed to thermal energy bled or transferred from portions ofthe build material that are to become part of the final 3D object.

As used herein, the terms “negatively pattern,” “negatively patterning,”“negatively patterned,” etc. refer to the application of liquid(s)(e.g., the anti-coalescing agent) to portion(s) of the build materialthat are not to become part of the final 3D object. It is to beunderstood that “negatively patterning” may include applying the liquidon all or less than all of the build material that is not to become partof the final 3D object. As such, in some examples disclosed herein, theanti-coalescing agent may be used to negatively pattern i) portions thatsurround the build material that is to become part of the final 3Dobject, ii) features, such as apertures, notches, cut-outs, or otherareas where the build material is not supposed to fuse, or iii) acombination thereof. When the anti-coalescing agent is used, it is to beunderstood there may be some build material that is patterned with adetailing agent alone or that is non-patterned (i.e., neither theanti-coalescing agent, nor the fusing agent, nor the laser beam, nor thedetailing agent is applied thereon). In other examples disclosed herein,the anti-coalescing agent may be used to negatively pattern all of thebuild material that is not to become part of the final 3D object. Inthese examples, there is no build material that is non-patterned.

When the anti-coalescing agent is applied, the anti-coalescing polymerforms a polymeric coating on the surfaces of the build materialparticles and in the voids between the build material particles. Assuch, the negatively patterning of the build material with theanti-coalescing agent defines a removable build material portion thatcontains build material with altered surface properties which preventthe build material from coalescing with other build material during 3Dprinting. As used herein, the term “removable build material portion”refers to the polymeric coating and the polymeric or polymeric compositebuild material upon/among which the polymeric coating is formed, whichis removable from the final 3D object. As used herein, “upon” refers tothe polymeric coating formed on surfaces of the build materialparticles, and “among” refers to the polymeric coating present in voidsbetween the build material particles.

The polymeric coating prevents the build material, upon/among which thepolymeric coating is formed, from fusing or semi-fusing. Thus, thepolymeric coating may prevent the portions of the build material thatare not to become part of the final 3D object, but that are exposed tobled or transferred thermal energy, from fusing to the final 3D object.As such, the printing process produces i) the final 3D object withimproved surface finish quality and/or accuracy (as compared to a 3Dobject printed according to a comparable method for 3D printing butwithout using the anti-coalescing agent) and ii) a removable object incontact with at least a portion of the final 3D object.

As used herein, the term “removable object” refers to the sum of theremovable build material portions that are formed throughout theprinting process. As such, the removable object includes the polymericcoating and the polymeric or polymeric composite build materialparticles upon/among which the polymeric coating is formed. It is to beunderstood that the removable build material portions that make up theremovable object may be contiguous or may be separated from each other(e.g., by the final 3D object). After printing, the removable object maybe removed from the final 3D object.

In the examples disclosed herein, the anti-coalescing agent includes thevehicle and the anti-coalescing polymer dispersed in the vehicle. Insome examples, the anti-coalescing agent for the three-dimensional (3D)printing process, comprises: a vehicle, comprising: a co-solvent; asurfactant; a humectant; and water; and an anti-coalescing polymerdispersed in the vehicle, the anti-coalescing polymer having a meanparticle size ranging from about 50 nm to about 195 nm, and theanti-coalescing polymer to coat polymeric build material particles toprevent the polymeric build material particles from fusing duringelectromagnetic radiation exposure of the 3D printing process. In theseexamples, the anti-coalescing agent may include additional components.

In another example, the anti-coalescing agent consists of: the vehicle,comprising: a co-solvent; a surfactant; a humectant; and water; and ananti-coalescing polymer dispersed in the vehicle, the anti-coalescingpolymer having a mean particle size ranging from about 50 nm to about195 nm, and the anti-coalescing polymer to coat polymeric build materialparticles to prevent the polymeric build material particles from fusingduring electromagnetic radiation exposure of the 3D printing process. Inthese examples, the anti-coalescing agent does not include anyadditional components.

The anti-coalescing polymer may be any polymer capable of coatingpolymeric build material particles and capable of preventing thepolymeric build material particles, fibers, etc. from coalescing (e.g.,fusing, thermally merging, etc.) during electromagnetic radiationexposure of a 3D printing process. In an example, the anti-coalescingpolymer has a mean particle size ranging from about 50 nm to about 195nm. The term “particle size”, as used herein, refers to the diameter ofa spherical particle, or the average diameter of a non-sphericalparticle (i.e., the average of multiple diameters across the particle),or the volume-weighted mean diameter of a particle distribution.

In some examples, the anti-coalescing polymer is a perfluorinatedpolymer. It has been found that perfluorinated polymers are capable ofboth forming a coating on the build material and of keeping the buildmaterial from coalescing when heated to a temperature that wouldotherwise cause the material to coalesce. In one of these examples, theperfluorinated polymer is selected from the group consisting of aperfluoroalkoxy alkane, poly(tetrafluoroethylene), a perfluorinatedpolyether, fluorinated ethylene propylene, and combinations thereof.Examples of a perfluoroalkoxy alkane have a chemical structure of:

where n is greater than 5 and less than 100,000 and m is greater than 5and less than 100,000. Examples of a poly(tetrafluoroethylene) have achemical structure of:

where n is greater than 5 and less than 100,000. An example ofpoly(tetrafluoroethylene) includes TEFLON® (available from E. I. du Pontde Nemours and Company). Examples of a perfluorinated polyether have achemical structure of:

where n is greater than 5 and less than 100,000. In some examples of theperfluorinated polyether, n ranges from 10 to 60. Examples of aperfluorinated polyether include KRYTOX™ lubricants (available from TheChemours Company). Examples of fluorinated ethylene propylene have achemical structure of:

where n is greater than 5 and less than 100,000 and m is greater than 5and less than 100,000.

In an example, the anti-coalescing polymer is included in theanti-coalescing agent in an amount ranging from about 2 wt % to about 30wt %, based on the total weight of the anti-coalescing agent. In anotherexample, the anti-coalescing polymer is included in the anti-coalescingagent in an amount ranging from about 3 wt % to about 10 wt %, based onthe total weight of the anti-coalescing polymer agent.

The anti-coalescing polymer is selected so that it will form thepolymeric coating. The polymeric coating may form before the vehicleevaporates (i.e., as the anti-coalescing agent penetrated into the buildmaterial), or as the vehicle evaporates, or after the vehicleevaporates, or combinations thereof. The polymeric coating enables thebuild material within the removable build material portion to remainnon-fused, and thus separable from layers of the final 3D object. Thepolymeric coating changes the surface properties of the polymeric orpolymeric composite build material in the removable build materialportion such that the anti-coalescing polymer coated build material doesnot fuse or coalesce. More particularly, the build material coated withthe polymeric coating (i.e., the build material particles in theremovable build material portion) do not fuse or coalesce with buildmaterial that is not coated with the polymeric coating (e.g., thepolymeric or polymeric composite build material in the portion that isto form part of the final 3D object) nor with other build material thatis coated with the polymeric coating. In an example, the build materialparticles coated with the polymeric coating do not coalesce (e.g., byfusing, melting, thermally migrating, etc.) even when heated to atemperature at or above the melting temperature of the polymeric orpolymeric composite build material.

As mentioned above, the anti-coalescing agent also includes the vehicle.As used herein, “vehicle” may refer to the liquid in which theanti-coalescing polymer is dispersed to form the anti-coalescing agent.In some examples, the vehicle includes a co-solvent, a surfactant, ahumectant, and water. In these examples, the vehicle may includeadditional components, such as anti-kogation agent(s), antimicrobialagent(s), and/or chelating agent(s), each of which is described below inreference to the fusing agent. In other examples, the vehicle consistsof a co-solvent, a surfactant, a humectant, and water without any othercomponents.

Water may make up the balance of the anti-coalescing agent. As such, theamount of water may vary depending upon the amounts of the othercomponents that are included. As an example, deionized water may beused.

The vehicle may also include co-solvent(s). In an example, the totalamount of the co-solvent(s) present in the anti-coalescing agent rangesfrom about 10 wt % to about 20 wt %, based on the total weight of theanti-coalescing agent.

Classes of organic co-solvents that may be used in the vehicle includealiphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycolethers, 2-pyrrolidones, caprolactams, formamides, acetamides, glycols,and long chain alcohols. Examples of these co-solvents include primaryaliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols,1,3-alcohols, 1,5-alcohols, 1,6-hexanediol or other diols (e.g.,1,5-pentanediol, 2-methyl-1,3-propanediol, etc.), ethylene glycol alkylethers, propylene glycol alkyl ethers, higher homologs (C₆-C₁₂) ofpolyethylene glycol alkyl ethers, triethylene glycol, tetraethyleneglycol, tripropylene glycol methyl ether, N-alkyl caprolactams,unsubstituted caprolactams, both substituted and unsubstitutedformamides, both substituted and unsubstituted acetamides, and the like.Other examples of organic co-solvents include dimethyl sulfoxide (DMSO),isopropyl alcohol, ethanol, pentanol, acetone, or the like.

Other examples of suitable co-solvents include water-solublehigh-boiling point solvents, which have a boiling point of at least 120°C., or higher. Some examples of high-boiling point solvents include2-pyrrolidone (i.e., 2-pyrrolidinone, boiling point of about 245° C.),1-methyl-2-pyrrolidone (boiling point of about 203° C.),N-(2-hydroxyethyl)-2-pyrrolidone (boiling point of about 140° C.),2-methyl-1,3-propanediol (boiling point of about 212° C.), andcombinations thereof.

The co-solvent(s) of the vehicle may depend, in part upon the jettingtechnology that is to be used to dispense the anti-coalescing agent. Forexample, if thermal inkjet printheads are to be used, water and/orethanol and/or other longer chain alcohols (e.g., pentanol) may make up35 wt % or more of the anti-coalescing agent. For another example, ifpiezoelectric inkjet printheads are to be used, water may make up fromabout 25 wt % to about 30 wt % of the anti-coalescing agent, and 35 wt %or more of the anti-coalescing agent may be ethanol, isopropanol,acetone, etc.

The vehicle may include surfactant(s) to improve the jettability of theanti-coalescing agent. In an example, the total amount of thesurfactant(s) present in the anti-coalescing agent ranges from about0.25 wt % to about 3 wt %, based on the total weight of theanti-coalescing agent.

In an example, the vehicle includes a blend of surfactants. The blendmay include non-ionic surfactant(s) and anionic surfactant(s). As oneexample, the blend includes three different non-ionic surfactants andone anionic surfactant. For example, the surfactants include a firstnon-ionic surfactant having a first hydrophilic chain length; a secondnon-ionic surfactant having a second hydrophilic chain length that isdifferent than the first hydrophilic chain length; a third non-ionicsurfactant, wherein the third non-ionic surfactant is selected from thegroup consisting of a polyether siloxane and an alkoxylated alcohol; andan anionic surfactant. More specifically, the first non-ionic surfactantmay be TERGITOL™ TMN-6 (available from The Dow Chemical Company), thesecond non-ionic surfactant may be TERGITOL™ 15-S-30 (which has a higherHLB number and a longer hydrophilic chain length than TERGITOL™ TMN-6),the third non-ionic surfactant is a polyether siloxane (e.g., TEGO® Wet270 or TEGO® Wet 280, available from Evonik) or an alkoxylated alcohol(e.g., TEGO® Wet 510 available from Evonik), and anionic surfactant maybe alkyldiphenyloxide disulfonate (e.g., the DOWFAX™ series, such a 2A1,3B2, 8390, C6L, C10L, and 30599). The first non-ionic surfactant and thesecond non-ionic surfactant may also be selected from the IGEPAL® series(available from Rhodia), the PLURONIC® series (available from BASFCorp.), the TRITON™ series (available from The Dow Chemical Company),the ECOSURF™ EH series (available from The Dow Chemical Company), andthe ECOSURF™ SA series (available from The Dow Chemical Company), aslong as the two non-ionic surfactants have different hydrophilic chainlengths.

A balance of the non-ionic surfactants and the anionic surfactant allowsfor better stabilization of all of the components and balance of thetotal surface tension of the anti-coalescing agent. In some examples,the first non-ionic surfactant may be present in an amount ranging fromabout 0.1 wt % to about 1 wt %; the second non-ionic surfactant may bepresent in an amount ranging from about 0.1 wt % to about 1 wt %; thethird non-ionic surfactant may be present in an amount ranging fromabout 0.1 wt % to about 1 wt %; and/or the anionic surfactant may bepresent in an amount ranging from about 0.1 wt % to about 1 wt % (basedon the total weight of the anti-coalescing agent).

In other examples, the non-ionic surfactants of the surfactant blend maybe replaced with other non-ionic surfactants, such as aself-emulsifiable, non-ionic wetting agent based on acetylenic diolchemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc.),and/or an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 465,SURFYNOL® 440 or SURFYNOL® CT-111 from Air Products and Chemical Inc.),and/or an ethoxylated wetting agent and molecular defoamer (e.g.,SURFYNOL® 420 from Air Products and Chemical Inc.). Still other suitablenon-ionic surfactants include non-ionic wetting agents and moleculardefoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc.) orwater-soluble, non-ionic surfactants (e.g., TERGITOL™ TMN-6, TERGITOL™15-S-7, TERGITOL™ 15-S-9, or TERGITOL™ 15-S-30 (a secondary alcoholethoxylate) from The Dow Chemical Company). Another suitable non-ionicsurfactant is an alkoxylated alcohol, such as TECO® Wet 510 availablefrom Evonik.

In still other examples, the surfactant may be a fluorosurfactant. As anexample, a non-ionic fluorosurfactant (e.g., CAPSTONE®fluorosurfactants, such as CAPSTONE® FS-35, from E. I. du Pont deNemours and Company, previously known as ZONYL FSO) may be used.

The vehicle may also include humectant(s). In an example, the totalamount of the humectant(s) present in the anti-coalescing agent rangesfrom about 3 wt % to about 10 wt %, based on the total weight of theanti-coalescing agent. An example of a suitable humectant is LIPONIC®EG-1 (i.e., LEG-1, glycereth-26, ethoxylated glycerol, available fromLipo Chemicals).

In an example, the anti-coalescing agent has a surface tension rangingfrom about 20 dynes/cm to about 28 dynes/cm. A surface tension withinthis range is desirable, as it may allow the anti-coalescing agent (andthus, the anti-coalescing polymer) to penetrate an entire layer of buildmaterial, which may allow the anti-coalescing polymer to form thepolymeric coating on all or substantially all of the build materialparticles in the some of the build material that becomes the removablebuild material portion. While the selection of the anti-coalescingpolymer provides the coated build material of the removable buildmaterial portion with the ability to remain intact (i.e., non-coalesced)upon heat/energy exposure, it is to be understood that the surfacetension of the anti-coalescing agent within this range may assist in theplacement of the anti-coalescing polymer in desirable locations within alayer of build material and upon the surfaces of the build material.

Referring now to FIG. 1 and FIGS. 2A through 2E, examples of a method100, 200 for three-dimensional (3D) printing are depicted. Prior toexecution of the method 100, 200 or as part of the method 100, 200 acontroller 54 (see, e.g., FIG. 4) may access data stored in a data store56 (see, e.g., FIG. 4) pertaining to a 3D object that is to be printed.The controller 54 may determine the number of layers of polymeric orpolymeric composite build material 16 that are to be formed, and thelocations at which the anti-coalescing agent 28 from the applicator 24Bis to be deposited on each of the respective layers.

As shown in FIG. 1, an example of the three-dimensional (3D) printingmethod 100 comprises: applying a polymeric or polymeric composite buildmaterial 16 (reference numeral 102); negatively patterning some 34′ ofthe polymeric or polymeric composite build material 16 to define aremovable build material portion 34 and a remaining build materialportion, the negatively patterning including: selectively applying ananti-coalescing agent 28 comprising: a vehicle, comprising: aco-solvent; a surfactant; a humectant; and water; and an anti-coalescingpolymer dispersed in the vehicle, the anti-coalescing polymer having amean particle size ranging from about 50 nm to about 195 nm (referencenumeral 104); based on a 3D object model, forming a layer 42 of a final3D object 44 from at least some 32 of the remaining build materialportion, wherein the some 34′ of the polymeric or polymeric compositebuild material 16 in the removable build material portion 34 remainsnon-coalesced (reference numeral 106).

As shown at reference numeral 102 in FIG. 1 and in FIGS. 2A and 2B, themethod 100, 200, includes applying the polymeric or polymeric compositebuild material 16. In the example shown in FIGS. 2A and 2B, a printingsystem (e.g., printing system 10 shown in FIG. 4) may be used to applythe build material 16. The printing system 10 may include a build areaplatform 12, a build material supply 14 containing build materialparticles 16, and a build material distributor 18.

The build area platform 12 receives the build material 16 from the buildmaterial supply 14. The build area platform 12 may be moved in thedirections as denoted by the arrow 20, e.g., along the z-axis, so thatthe build material 16 may be delivered to the build area platform 12 orto a previously formed layer 42. In an example, when the build materialparticles 16 are to be delivered, the build area platform 12 may beprogrammed to advance (e.g., downward) enough so that the build materialdistributor 18 can push the build material particles 16 onto the buildarea platform 12 to form a substantially uniform layer 40 of buildmaterial 16 thereon. The build area platform 12 may also be returned toits original position, for example, when a new part is to be built.

The build material supply 14 may be a container, bed, or other surfacethat is to position the build material particles 16 between the buildmaterial distributor 18 and the build area platform 12.

The build material distributor 18 may be moved in the directions asdenoted by the arrow 22, e.g., along the y-axis, over the build materialsupply 14 and across the build area platform 12 to spread the layer 40of the build material 16 over the build area platform 12. The buildmaterial distributor 18 may also be returned to a position adjacent tothe build material supply 14 following the spreading of the buildmaterial particles 16. The build material distributor 18 may be a blade(e.g., a doctor blade), a roller, a combination of a roller and a blade,and/or any other device capable of spreading the build material 16 overthe build area platform 12. For instance, the build material distributor18 may be a counter-rotating roller. In some examples, the buildmaterial supply 14 or a portion of the build material supply 14 maytranslate along with the build material distributor 18 such that buildmaterial 16 is delivered continuously to the material distributor 18rather than being supplied from a single location at the side of theprinting system 10 as depicted in FIG. 2A.

As shown in FIG. 2A, the build material supply 14 may supply the buildmaterial particles 16 into a position so that they are ready to bespread onto the build area platform 12. The build material distributor18 may spread the supplied build material particles 16 onto the buildarea platform 12. The controller 54 may process control build materialsupply data, and in response control the build material supply 14 toappropriately position the build material particles 16, and may processcontrol spreader data, and in response, control the build materialdistributor 18 to spread the supplied build material particles 16 overthe build area platform 12 to form the layer 40 of build material 16thereon. As shown in FIG. 2B, one build material layer 40 has beenformed.

The layer 40 of polymeric or polymeric composite build material 16 has asubstantially uniform thickness across the build area platform 12. In anexample, the thickness of the build material layer 40 is about 100 μm.In another example, the thickness of the build material layer 40 rangesfrom about 30 μm to about 300 μm, although thinner or thicker layers mayalso be used. For example, the thickness of the build material layer 40may range from about 20 μm to about 500 μm, or from about 50 μm to about80 μm. The layer thickness may be about 2× (i.e., 2 times) the particlediameter (as shown in FIG. 2B) at a minimum for finer part definition.In some examples, the layer thickness may be about 1.5× the particlediameter.

After the build material 16 has been applied, and prior to furtherprocessing, the build material layer 40 may be exposed to heating.Heating may be performed to pre-heat the build material particles 16,and thus the heating temperature may be below the melting point orsoftening point of the polymeric or polymeric composite build materialparticles 16. As such, the temperature selected will depend upon thepolymeric or polymeric composite build material particles 16 that areused. As examples, the pre-heating temperature may be from about 5° C.to about 50° C. below the melting point or softening point of thepolymeric or polymeric composite build material particles 16. In anexample, the pre-heating temperature ranges from about 50° C. to about250° C. In another example, the pre-heating temperature ranges fromabout 150° C. to about 170° C.

Pre-heating the layer 40 of the build material particles 16 may beaccomplished using any suitable heat source that exposes all of thepolymeric or polymeric composite build material particles 16 on thebuild area platform 12 to the heat. Examples of the heat source includea thermal heat source (e.g., a heater (not shown) integrated into thebuild area platform 12 (which may include sidewalls)) or the radiationsource 50, 50′ (see, e.g., FIG. 4).

As shown at reference numeral 104 in FIG. 1 and FIG. 2C, the method 100,200 continues by negatively patterning some 34′ of the polymeric orpolymeric composite build material 16 to define the removable buildmaterial portion 34 and the remaining build material portion. Once theanti-coalescing agent 28 is applied to some 34′ of the build material16, the polymeric coating 38 is formed on the surfaces of the some 34′of the build material particles 16 and is present in at least some ofthe voids between the some 34′ of the build material particles 16, andthis forms the removable build material portion 34. As such, theremovable build material portion 34 includes the polymeric coating 38and any build material particles 16 upon/among which the polymericcoating is formed.

The remaining build material portion includes any build material 16 thatis not negatively patterned with the anti-coalescing agent 28. At leastsome 32 of the remaining build material portion is to form the layer 42of the final 3D object 44 (shown in FIG. 4). In some examples, all ofthe remaining build material portion will form the layer 42. In otherexamples, the remaining build material portion may also include anotherportion 36 (also referred to herein as the third portion), which is notto form the layer 42 of the final 3D object 44. In some examples, thethird portion 36 may be non-patterned (i.e., may have no liquid appliedthereto).

In an example, the removable build material portion 34 is at leastpartially adjacent to the at least some 32 of the remaining buildmaterial portion. In another example, the removable build materialportion 34 includes i) portions of the build material 16 that surroundthe at least some 32 of the remaining build material portion, ii)features, such as apertures, notches, cut-outs, or other areas where thebuild material 16 is not supposed to fuse, or iii) a combinationthereof.

An example of this is shown in FIG. 3 (top view of the build material 16on the build area platform 12). In the example shown in this figure, theshape of the final 3D object layer to be formed is a cube or arectangular prism, and the pattern of the cross-section that is parallelto the surface of the build area platform 12 is a square or rectanglehaving an edge boundary 33. The build material 16 within the edgeboundary 33 is the at least some 32 of the remaining build materialportion which forms the layer 42 of the final 3D object 44. In theexample shown in FIG. 3, the at least some 32 of the remaining buildmaterial portion has the fusing agent 26 applied thereon. The buildmaterial 16 positioned along the outside of the edge boundary 33 is thebuild material 16 within the removable build material portion 34, andthus, is coated with the polymeric coating 38. The build material 16positioned outside of the removable build material portion 34 is thebuild material 16 within the third portion 36, and thus, may benon-patterned or may have a detailing agent 52 (see, e.g., FIG. 4)applied thereon. In the example shown in FIG. 3, the third portion 36has the detailing agent 52 applied thereon.

As shown in FIG. 2C, the negatively patterning includes selectivelyapplying the anti-coalescing agent 28. As mentioned above, theanti-coalescing agent 28 includes the vehicle and the anti-coalescingpolymer dispersed in the vehicle. In an example of the method 100, 200the anti-coalescing polymer is a perfluorinated polymer selected fromthe group consisting of a perfluoroalkoxy alkane,poly(tetrafluoroethylene), a perfluorinated polyether, fluorinatedethylene propylene, and combinations thereof.

As illustrated in FIG. 2C, the anti-coalescing agent 28 may be dispensedfrom the second applicator 24B. The applicator 24B may be a thermalinkjet printhead, a piezoelectric printhead, a continuous inkjetprinthead, etc., and the selectively applying of the anti-coalescingagent 28 may be accomplished by thermal inkjet printing, piezo electricinkjet printing, continuous inkjet printing, etc.

The controller 54 may process data, and in response, control the secondapplicator 24B (e.g., in the directions indicated by the arrow 38) todeposit the anti-coalescing agent 28 to define the removable buildmaterial portion 34 and the remaining build material portion. The secondapplicator 24B may be programmed to receive commands from the controller54 and to deposit the anti-coalescing agent 28 according to a pattern ofa cross-section for the removable build material portion 34. In theexample shown in FIG. 2C, the second applicator 24B selectively appliesthe anti-coalescing agent 28 to the build material 16 that is to be partof the removable build material portion 34. In the example shown in FIG.2C, the anti-coalescing agent 28 is deposited on the some 34′ of thebuild material 16 and not on the at least some 32 of the remaining buildmaterial portion or the third portion 36.

When the anti-coalescing agent 28 is selectively applied, theanti-coalescing polymer (present in the anti-coalescing agent 28) formsthe polymeric coating 38, on the surfaces of the build materialparticles 16 and in the voids between the build material particles 16,in the removable build material portion 34. The volume of theanti-coalescing agent 28 that is applied per unit of the build material16 may be sufficient to achieve the polymeric coating 38 that enablesthe build material 16 in the removable build material portion 34 toremain non-coalesced even after exposure to heating during the 3Dprinting process. In an example, the volume of the anti-coalescing agent28 that is applied may establish a desired coating density and/orthickness of the polymeric coating 38. As such, the polymeric coating 38may prevent the build material particles 16 upon/among which it isformed from fusing or semi-fusing.

As shown at reference numeral 106, the method 100, 200 continues byforming the layer 42 of the final 3D object 44 from the at least some 32of the remaining build material portion. The formation of the layer 42may be based on a 3D object model of the final 3D object 44.

In one example of the method 100, the forming of the layer 42 involvesselectively laser sintering, based on the 3D object model, the at leastsome 32 of the remaining build material portion. In these examples, alaser beam is used to selectively apply radiation to the at least some32 of the remaining build material portion. The laser beam may beapplied with the source 50 of radiation.

When the forming of the layer 42 involves selectively laser sintering(SLS), the removable build material portion 34 is negatively patternedfirst, and then the energy beam is selectively applied to the at leastsome 32 of the remaining build material portion.

In SLS, the energy beam may be supplied from the source 50, which may bea tightly focused energy source, such as a laser, electron beam ormicrowave tip emitter.

The controller 54 may process data, and in response, control the source50 of radiation (e.g., in the directions indicated by the arrow 58and/or in directions along the X-axis) to apply radiation to the atleast some 32 of the remaining build material portion that is to becomepart of the final 3D object 44. The source 50 may be attached to ascanning system that allows the source 50 to be moved into a desirableposition so that the energy beam is selectively applied to the at leastsome 32 of the remaining build material portion where it is desirable toform the layer 42. In an example, the tightly focused energy source 50and the scanning system may be attached to a moving XY stage or atranslational carriage 60 (see, e.g., FIG. 4) that moves them adjacentto the layer 40 in order to direct the energy beam in desirable area(s).Depending, in part, on the dimensions of the energy source 50 and thearea of the build material 16 to be fused (i.e., some 32), the tightlyfocused energy source 50 may have to be moved in order to create thelayer 42. For example, the source 50 may be programmed to receivecommands from the controller 54 and to apply the radiation according toa pattern of a cross-section for the layer 42 of the final 3D object 44that is to be formed. The scanning system may move the source 50 into asuitable position with respect to the some 32 of the remaining buildmaterial portion in order to create the layer 42. In other examples, thetightly focused energy source 50 and the scanning system may be fixedwhile a support member (similar to the build area platform 12) isconfigured to move relative thereto.

The amount of energy that is applied per unit of the build material 16in the at least some 32 of the remaining build material portion and/orthe time of exposure may be sufficient to cause the build material 16 inthe portion 32 to fuse. The amount of energy that is applied per unit ofthe build material 16 and/or the exposure time may depend, at least inpart, on the source 50 of radiation used, the energy of the radiationapplied, the wavelength of the radiation applied, and the build material16 used.

The build material 16 that is exposed to energy from the tightly focusedenergy source 50 fuses. The selective application of the energy heatsthe polymeric or polymeric composite build material particles 16. In anexample, the selective application of the radiation sufficientlyelevates the temperature of the polymeric or polymeric composite buildmaterial particles 16 in the layer 40 above the melting or softeningpoint of the particles 16, allowing fusing (e.g., melting, binding,etc.) of the polymeric or polymeric composite build material particles16 to take place. The selective application of the radiation forms thefused layer 42.

In another example of the method 100, 200, the forming of the layer 42involves: based on the 3D object model, selectively applying a fusingagent 26 on the at least some 32 of the remaining build materialportion; and exposing the polymeric or polymeric composite buildmaterial 16 to radiation to fuse the at least some 32 of the remainingbuild material portion. The fusing agent 26 includes a radiationabsorber. The composition of the fusing agent 26 will be described inmore detail below.

As illustrated in FIG. 2D, the fusing agent 26 may be dispensed from thefirst applicator 24A (which may be similar to applicator 24B) to patternthe at least some 32 of the remaining build material portion. In anexample, the removable build material portion 34 may be negativelypatterned first, and then the at least some 32 of the remaining buildmaterial portion may be patterned. In another example, the at least some32 of the remaining build material portion may be patterned first, andthen the removable build material portion 34 may be negativelypatterned. In still another example, the at least some 32 of theremaining build material portion may be patterned and the removablebuild material portion 34 may be negatively patterned at leastsubstantially simultaneously (e.g., at the same time). In all of theseexamples, the removable build material portion 34 is negativelypatterned before the build material 16 is exposed to radiation.

The controller 54 may process data, and in response, control the firstapplicator 24A (e.g., in the directions indicated by the arrow 58) todeposit the fusing agent 26 onto the at least some 32 of the remainingbuild material portion that is to become part of the final 3D object 44.The first applicator 24A may be programmed to receive commands from thecontroller 54 and to deposit the fusing agent 26 according to a patternof a cross-section for the layer 42 of the final 3D object 44 that is tobe formed. In the example shown in FIG. 2D, the first applicator 24Aselectively applies the fusing agent 26 on the at least some 32 of theremaining build material portion of the layer 40 that is to become thefirst layer 42 of the final 3D object 44. In the example shown in FIG.2D, the fusing agent 26 is deposited on the at least some 32 of theremaining build material portion of the layer 40 and not on theremovable build material portion 34 or the third portion 36.

As mentioned above, the fusing agent 26 includes the radiation absorber.The volume of the fusing agent 26 that is applied per unit of the buildmaterial 16 in the at least some 32 of the remaining build materialportion may be sufficient to absorb and convert enough radiation so thatthe build material 16 in the patterned portion 32 will fuse. The volumeof the fusing agent 26 that is applied per unit of the build material 16may depend, at least in part, on the radiation absorber used, theradiation absorber loading in the fusing agent 26, and the buildmaterial 16 used.

After the fusing agent 26 is selectively applied, the build material 16is exposed to radiation to fuse the at least some 32 of the remainingbuild material portion. The radiation may be applied with the source 50,50′ of radiation.

The fusing agent 26 enhances the absorption of the radiation, convertsthe absorbed radiation to thermal energy, and promotes the transfer ofthe thermal heat to the polymeric or polymeric composite build materialparticles 16 in contact therewith. In an example, the fusing agent 26sufficiently elevates the temperature of the build material particles 16in the layer 40 above the melting or softening point of the particles16, allowing coalescing (e.g., fusing, thermal merging, melting,binding, etc.) of the polymeric or polymeric composite build materialparticles 16 to take place. The application of the radiation forms thefused layer 42, shown in FIG. 2E.

Whether the energy beam (e.g., SLS) or the combination of the fusingagent 26 and applied radiation is used, it is to be understood that thebuild material 16 in the removable build material portion 34 does notfuse or semi-fuse to the layer 42. As shown in FIG. 2E, the removablebuild material portion 34 remains physically separable from the layer42. The polymeric coating 38 maintains the separation between the buildmaterial 16 in the removable build material portion 34 and the fusedlayer 42. As such, the polymeric coating 38 prevents the fusing orsemi-fusing of the build material 16 in the removable build materialportion 34 to the surface of the final 3D object 44. Thus, the final 3Dobject 44 may have improved surface finish quality and/or accuracy (ascompared to a 3D object printed according to a comparable method for 3Dprinting but without using the anti-coalescing agent 28).

In some examples, the build material 16 in the removable build materialportion 34 reaches a temperature at or above the melting temperature ofthe polymeric or polymeric composite build material 16. In theseexamples, the polymeric coating 38 still maintains the separationbetween the build material 16 in the removable build material portion 34and the fused layer 42. As such, the polymeric coating 38 changes thesurface properties of the build material particles 16 in the removablebuild material portion 34 such that the particles 16 do not coalesce,i.e., fuse, melt, thermally merge, etc. together, during heating.

In some examples, the method 100, 200 further comprises repeating theapplying of the polymeric or polymeric composite build material 16, thenegatively patterning, and the forming, wherein the repeating forms i)the final 3D object 44 including the layer 42 and ii) a removable object46 (see, e.g., FIG. 4) in contact with at least a portion of the final3D object 44, the removable object 46 including the removable buildmaterial portion 34.

In these examples, a three-dimensional (3D) printed article 48 (see,e.g., FIG. 4) may be formed. In an example, the three-dimensional (3D)printed article 48 comprises: a fused polymer or polymer compositeobject 44; and a removable object 46 in contact with at least a portionof the fused polymer or polymer composite object 44, the removableobject 46 comprising: polymeric or polymeric composite build materialparticles 16; and a polymeric coating 38 formed on surfaces of thepolymeric or polymeric composite build material particles 16 and presentin voids between the polymeric or polymeric composite build materialparticles 16, wherein the polymeric coating 38 is a perfluorinatedpolymer. In this example, the perfluorinated polymer may be selectedfrom the group consisting of a perfluoroalkoxy alkane,poly(tetrafluoroethylene), a perfluorinated polyether, fluorinatedethylene propylene, and combinations thereof.

In an example, the removable object 46 at least partially surrounds thefinal 3D object 44. In another example, the final 3D object 44 at leastpartially surrounds the removable object 46 (e.g., once removed, theremovable object 46 will form a notch, aperture, etc. in the final 3Dobject 44). In still another example, the removable build materialportion 34 is located outside of an edge of the remaining build materialportion or is at least partially surrounded by the remaining buildmaterial portion.

The removable object 46 may be removed from the final 3D object 44 byany suitable means. In an example, the removable object 46 may beremoved from the final 3D object 44 by lifting the final 3D object 44from the removable object 46. In some examples, the removable object 46may be broken into pieces and removed piecewise from the final 3D objet44. In some other examples, a removal tool may be used. In still otherexamples, the removable object 46 may be removed from the final 3Dobject 44 using a wet or a dry removal process. In an example, the wetremoval process may include spraying the removable object 46 with wateror another liquid using wet removal tool(s), such as a hose and asprayer, a spray gun, etc. In other examples, the wet removal processmay include sonicating the removable object 46 in a water bath orsoaking the removable object 46 in water or another liquid. In someexamples, dry removal of the removable object 46 from the final 3Dobject 44 may be used. As an example, the removable object 46 may beremoved from the final 3D object 44 by suction from a vacuum hose.Pieces of the removable object 46 that remain in contact with the final3D object 44 may be removed by light bead blasting or cleaning with abrush and/or an air jet.

Several variations of the previously described method 100, 200 will nowbe described.

In some examples, it may be desirable to apply the laser beam to theremovable build material portion 34 or to apply the fusing agent 26 onthe removable build material portion 34, so that during the exposing ofthe build material 16 to energy/radiation, the removable build materialportion 34 is heated to a temperature at or above the meltingtemperature of the polymeric or polymeric composite build material 16.Heating the removable build material portion 34 to such a temperaturemay prevent or reduce the formation of thermal gradients during thefusing of the layer 42. The formation of thermal gradients may beundesirable because they may cause surface defects and/or shrinkageeffects in the final 3D object 44.

As such, in some examples, the method 100, 200 further comprisesselectively applying the fusing agent 26 on the removable build materialportion 34. In these examples, the anti-coalescing agent 28 is appliedon the some 34′ of the build material first, and then the fusing agent26 is applied on the same some 34′ of the build material 16 in theremovable build material portion 34. If the fusing agent 26 is appliedon the some 34′ of the build material 16 before the anti-coalescingagent 28 is applied, then energy (from pre-heating, from a previouslayer, etc.) may cause the some 34′ of the build material to coalesce(e.g., fuse or semi-fuse) after the fusing agent 26 is applied andbefore the anti-coalescing agent 28 is applied.

In other examples, the method 100, 200 further comprises selectivelyapplying the energy beam on the removable build material portion 34.When the fusing agent 26 or the energy beam is applied on the removablebuild material portion 34, an amount of the fusing agent 26 applied orthe amount of the energy applied (from the laser beam) may be less thanthe amount applied on the at least some 32 of the remaining buildmaterial portion. Alternatively, a greater amount (e.g., 40 g/m²) of theanti-coalescing agent 28 may be applied then would be applied if thefusing agent 26 or the energy beam were not to be applied on theremovable build material portion 34.

In other examples of the method 100, 200, a detailing agent 52 may beused. In some examples, the detailing agent 52 may include a surfactant,a co-solvent, and water. The composition of the detailing agent 52 willbe described in more detail below. The detailing agent 52 may bedispensed from another (e.g., a third) applicator 24C (which may besimilar to applicators 24A, 24B) and applied to portion(s) of the buildmaterial 16.

The detailing agent 52 may provide an evaporative cooling effect to thebuild material 16 to which it is applied. The cooling effect of thedetailing agent 52 reduces the temperature of the polymeric or polymericcomposite build material 16 containing the detailing agent 52 duringenergy/radiation exposure. The detailing agent 52, and its rapid coolingeffect, may be used to obtain different levels of melting/fusing/bindingwithin the layer 42 of the 3D object 44 that is being formed. Differentlevels of melting/fusing/binding may be desirable to control internalstress distribution, warpage, mechanical strength performance, and/orelongation performance of the final 3D object 44.

In an example of using the detailing agent 52 to obtain different levelsof melting/fusing/binding within the layer 42, the fusing agent 26 maybe selectively applied according to the pattern of the cross-section forthe layer 42 of the 3D object 44, and the detailing agent 52 may beselectively applied within at least a portion of that cross-section. Assuch, some examples of the method 100, 200 further comprise selectivelyapplying the detailing agent 52 on the at least some 32 of the remainingbuild material portion, wherein the detailing agent 52 includes asurfactant, a co-solvent, and water. The evaporative cooling provided bythe detailing agent 52 may remove energy from the at least some 32 ofthe remaining build material portion; however, since the fusing agent 26is present with the detailing agent 52, fusing is not completelyprevented. The level of fusing may be altered due to the evaporativecooling, which may alter the internal stress distribution, warpage,mechanical strength performance, and/or elongation performance of the 3Dobject 44. It is to be understood that when the detailing agent 52 isapplied within the same portion as the fusing agent 26, the detailingagent 52 may be applied in any desirable pattern. When the fusing agent26 is used, the detailing agent 52 may be applied before, after, or atleast substantially simultaneously (e.g., one immediately after theother in a single printing pass, or at the same time) with the fusingagent 26, and then the build material 16 is exposed to radiation.

In another example of using the detailing agent 52 to obtain differentlevels of melting/fusing/binding within the layer 42, the detailingagent 52 may be applied on the at least some 32 of the remaining buildmaterial portion where the energy beam is applied to selectively fusethe at least some 32 of the remaining build material portion. When theenergy beam is used, the detailing agent 52 may be applied before theenergy beam is selectively applied.

In some examples, whether the fusing agent 26 and radiation exposure orthe energy beam is used to form the layer 42, the detailing agent 52 mayalso or alternatively be applied after the layer 42 is fused to controlthermal gradients within the layer 42 and/or the final 3D object 44. Inthese examples, the thermal gradients may be controlled with theevaporative cooling provided by the detailing agent 52.

In another example that utilizes the evaporative cooling effect of thedetailing agent 52, the method 100, 200 further comprises selectivelyapplying the detailing agent 52 on the third portion 36 of the polymericor polymeric composite build material 16 to prevent the polymeric orpolymeric composite build material 16 in the third portion 36 fromfusing, wherein the third portion 36 does not include the removablebuild material portion 34 or the at least some 32 of the remaining buildmaterial portion, and the detailing agent 52 includes a surfactant, aco-solvent, and water. The evaporative cooling provided by the detailingagent 52 may remove energy from the third portion 36, which may lowerthe temperature of the build material 16 in the third portion 36 andprevent the build material 16 in the third portion 36 from fusing.

The detailing agent 52 may also be used to improve the wetting of theanti-coalescing agent 28 on the build material 16. In this example, themethod 100, 200 further comprises selectively applying the detailingagent 52 on the some 34′ of the polymeric or polymeric composite buildmaterial 16 to at least partially facilitate wetting of theanti-coalescing agent 28 on the some 34′ of the polymeric or polymericcomposite build material 16, wherein the detailing agent 52 includes asurfactant, a co-solvent, and water. The detailing agent 52 may at leastpartially facilitate the penetration of the anti-coalescing polymer (inthe anti-coalescing agent 28) within the void spaces between the buildmaterial particles 16 and/or the wetting of the anti-coalescing polymeron the build material particles 16 to form the coating 38. When thedetailing agent 52 is applied on the some 34′ of the build material 16,the detailing agent 52 and the anti-coalescing agent 28 may be appliedat least substantially simultaneously (e.g., one immediately after theother in a single printing pass, or at the same time).

Referring now to FIG. 4, an example of a 3D printing system 10 isschematically depicted. It is to be understood that the 3D printingsystem 10 may include additional components (some of which are describedherein) and that some of the components described herein may be removedand/or modified.

Furthermore, components of the 3D printing system 10 depicted in FIG. 4may not be drawn to scale and thus, the 3D printing system 10 may have adifferent size and/or configuration other than as shown therein.

In an example, the three-dimensional (3D) printing system 10, comprises:a supply 14 of the polymeric or polymeric composite build material 16;the build material distributor 18; a supply of the anti-coalescing agent28 comprising: a vehicle, comprising: a co-solvent; a surfactant; ahumectant; and water; and an anti-coalescing polymer dispersed in thevehicle, the anti-coalescing polymer having a mean particle size rangingfrom about 50 nm to about 195 nm; the applicator 24B for selectivelydispensing the anti-coalescing agent 28; a source 50, 50′ of radiation;a controller 54; and a non-transitory computer readable medium havingstored thereon computer executable instructions to cause the controller54 to: utilize the build material distributor 18 to dispense thepolymeric or polymeric composite build material 16; utilize theapplicator 24B to selectively dispense anti-coalescing agent 28 tonegatively pattern some 34′ of the polymeric or polymeric compositebuild material and to define a removable build material portion 34 and aremaining build material portion; and utilize the source 50, 50′ ofradiation to form a layer 42 of a final 3D object 44 from at least some32 of the remaining build material portion, wherein the some 34′ of thepolymeric or polymeric composite build material 16 in the removablebuild material portion 34 remains non-coalesced.

As shown in FIG. 4, the printing system 10 includes the build areaplatform 12, the build material supply 14 containing the build material16, and the build material distributor 18.

As mentioned above, the build area platform 12 receives the buildmaterial 16 from the build material supply 14. The build area platform12 may be integrated with the printing system 10 or may be a componentthat is separately insertable into the printing system 10. For example,the build area platform 12 may be a module that is available separatelyfrom the printing system 10. The build material platform 12 that isshown is one example, and could be replaced with another support member,such as a platen, a fabrication/print bed, a glass plate, or anotherbuild surface.

As also mentioned above, the build material supply 14 may be acontainer, bed, or other surface that is to position the build material16 between the build material distributor 18 and the build area platform12. In some examples, the build material supply 14 may include a surfaceupon which the build material 16 may be supplied, for instance, from abuild material source (not shown) located above the build materialsupply 14. Examples of the build material source may include a hopper,an auger conveyer, or the like. Additionally, or alternatively, thebuild material supply 14 may include a mechanism (e.g., a deliverypiston) to provide, e.g., move, the build material 16 from a storagelocation to a position to be spread onto the build area platform 12 oronto a previously formed layer 42 of the final 3D object 44.

As also mentioned above, the build material distributor 18 may be ablade (e.g., a doctor blade), a roller, a combination of a roller and ablade, and/or any other device capable of spreading the build material16 over the build area platform 12 (e.g., a counter-rotating roller).

As shown in FIG. 4, the printing system 10 also includes the secondapplicator 24B, which may contain the anti-coalescing agent 28. As alsoshown in FIG. 4, the printing system 10 may also include the firstapplicator 24A, which may contain the fusing agent 26 and the thirdapplicator 24C, which may contain the detailing agent 52.

The applicators 24A, 24B, 24C may be scanned across the build areaplatform 12 in the direction indicated by the arrow 58, e.g., along they-axis. The applicators 24A, 24B, 24C may be, for instance, thermalinkjet printheads, piezoelectric printheads, continuous inkjetprintheads, etc., and may extend a width of the build area platform 12.While each of the applicators 24A, 24B, 24C is shown in FIG. 4 as asingle applicator, it is to be understood that each of the applicators24A, 24B, 24C may include multiple applicators that span the width ofthe build area platform 12. Additionally, the applicators 24A, 24B, 24Cmay be positioned in multiple printbars. The applicators 24A, 24B, 24Cmay also be scanned along the x-axis, for instance, in configurations inwhich the applicators 24A, 24B, 24C do not span the width of the buildarea platform 12 to enable the applicators 24A, 24B, 24C to respectivelydeposit the liquids 26, 28, 52 over a large area of a layer 40 of buildmaterial particles 16. The applicators 24A, 24B, 24C may thus beattached to a moving XY stage or a translational carriage 60 that movesthe applicators 24A, 24B, 24C adjacent to the build area platform 12 inorder to deposit the respective liquids 26, 28, 52 in the respectiveareas 32, 34, 36 of a layer 40 of the build material particles 16 thathas been formed on the build area platform 12 in accordance with themethod(s) 100, 200, disclosed herein. The applicators 24A, 24B, 24C mayinclude a plurality of nozzles (not shown) through which the respectiveliquids 26, 28, 52 are to be ejected.

The applicators 24A, 24B, 24C may deliver drops of the respectiveliquids 26, 28, 52 at a resolution ranging from about 300 dots per inch(DPI) to about 1200 DPI. In other examples, the applicators 24A, 24B,24C may deliver drops of the respective liquids 26, 28, 52 at a higheror lower resolution. The drop velocity may range from about 5 m/s toabout 24 m/s and the firing frequency may range from about 1 kHz toabout 100 kHz. In one example, each drop may be on the order of about 3picoliters (pl) to about 18 pl, although it is contemplated that ahigher or lower drop volume may be used. In some examples, theapplicators 24A, 24B, 24C are able to deliver variable size drops of therespective liquids 26, 28, 52. One example of a suitable printhead has600 DPI resolution and can deliver drop volumes ranging from about 6 plto about 14 pl.

Each of the previously described physical elements may be operativelyconnected to a controller 54 of the printing system 10. The controller54 may process print data that is based on a 3D object model of thefinal 3D object 44 to be generated. In response to data processing, thecontroller 54 may control the operations of the build area platform 12,the build material supply 14, the build material distributor 18, and theapplicators 24A, 24B, 24C. As an example, the controller 54 may controlactuators (not shown) to control various operations of the 3D printingsystem 10 components. The controller 54 may be a computing device, asemiconductor-based microprocessor, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), and/or another hardwaredevice. Although not shown, the controller 54 may be connected to the 3Dprinting system 10 components via communication lines.

The controller 54 manipulates and transforms data, which may berepresented as physical (electronic) quantities within the printer'sregisters and memories, in order to control the physical elements tocreate the final 3D object 44. As such, the controller 54 is depicted asbeing in communication with a data store 56. The data store 56 mayinclude data pertaining to a final 3D object 44 to be printed by the 3Dprinting system 10. The data for the selective delivery of the buildmaterial particles 16, the anti-coalescing agent 28, etc. may be derivedfrom a model of the final 3D object 44 to be formed. For instance, thedata may include the locations on each layer of build material particles16 that the second applicator 24B is to deposit the anti-coalescingagent 28. In one example, the controller 54 may use the data to controlthe second applicator 24B to selectively apply the anti-coalescing agent28. The data store 56 may also include machine readable instructions(stored on a non-transitory computer readable medium) that are to causethe controller 54 to control the amount of build material particles 16that is supplied by the build material supply 14, the movement of thebuild area platform 12, the movement of the build material distributor18, the movement of the applicators 24A, 24B, 24C, etc.

As shown in FIG. 4, the printing system 10 may also include a source 50,50′ of radiation. In some examples, the source 50′ of radiation may bein a fixed position with respect to the build material platform 12. Thesource 50′ in the fixed position may be a conductive heater or aradiative heater that is part of the printing system 10. These types ofheaters may be placed below the build area platform 12 (e.g., conductiveheating from below the platform 12) or may be placed above the buildarea platform 12 (e.g., radiative heating of the build material layersurface). In other examples, the source 50 of radiation may bepositioned to apply energy/radiation to the layer 40 of build materialparticles 16 immediately after the fusing agent 26 has been appliedthereto. In the example shown in FIG. 4, the source 50 of radiation isattached to the side of the applicators 24A, 24B, 24C which allows forpatterning and heating/exposing to radiation in a single pass.

In still other examples (not shown), the source 50 of radiation may be alaser or other tightly focused energy source that may selectively applyenergy to the layer 40 as previously described for SLS. The laser mayemit light through optical amplification based on the stimulatedemission of radiation. The laser may emit light coherently (i.e.,constant phase difference and frequency), which allows the radiation tobe emitted in the form of a laser beam that stays narrow over largedistances and focuses on a small area. In some example, the laser orother tightly focused energy source may be a pulse laser (i.e., theoptical power appears in pluses). Using a pulse laser allows energy tobuild between pluses, which enable the beam to have more energy. Asingle laser or multiple lasers may be used.

The source 50, 50′ of radiation may emit radiation having wavelengthsranging from about 100 nm to about 1 mm. As one example, the radiationmay range from about 800 nm to about 2 μm. As another example, theradiation may be blackbody radiation with a maximum intensity at awavelength of about 1100 nm. The source 50, 50′ of radiation may beinfrared (IR) or near-infrared light sources, such as IR or near-IRcuring lamps, IR or near-IR light emitting diodes (LED), or lasers withthe desirable IR or near-IR electromagnetic wavelengths.

The source 50, 50′ of radiation may be operatively connected to alamp/laser driver, an input/output temperature controller, andtemperature sensors, which are collectively shown as radiation systemcomponents 62. The radiation system components 62 may operate togetherto control the source 50, 50′ of radiation. The temperature recipe(e.g., radiation exposure rate) may be submitted to the input/outputtemperature controller. During heating, the temperature sensors maysense the temperature of the build material particles 16, and thetemperature measurements may be transmitted to the input/outputtemperature controller. For example, a thermometer associated with theheated area can provide temperature feedback. The input/outputtemperature controller may adjust the source 50, 50′ of radiation powerset points based on any difference between the recipe and the real-timemeasurements. These power set points are sent to the lamp/laser drivers,which transmit appropriate lamp/laser voltages to the source 50, 50′ ofradiation. This is one example of the radiation system components 62,and it is to be understood that other radiation source control systemsmay be used. For example, the controller 54 may be configured to controlthe source 50, 50′ of radiation.

In the examples of the method 100, 200 and the system 10 disclosedherein, the build material particles 16 may be a polymeric buildmaterial or a polymeric composite build material. As used herein, theterm “polymeric build material” may refer to crystalline orsemi-crystalline polymer particles. As used herein, the term “polymericcomposite build material” may refer to composite particles made up ofpolymer and ceramic.

Examples of semi-crystalline polymers include semi-crystallinethermoplastic materials with a wide processing window of greater than 5°C. (i.e., the temperature range between the melting point and there-crystallization temperature). Some specific examples of thesemi-crystalline thermoplastic materials include polyamides (PAs) (e.g.,PA 11/nylon 11, PA 12/nylon 12, PA 6/nylon 6, PA 8/nylon 8, PA 9/nylon9, PA 66/nylon 66, PA 612/nylon 612, PA 812/nylon 812, PA 912/nylon 912,etc.). Other examples of crystalline or semi-crystalline polymerssuitable for use as the build material particles 16 includepolyethylene, polypropylene, and polyoxomethylene (i.e., polyacetals).Still other examples of suitable build material particles 16 includepolystyrene, polycarbonate, polyester, polyurethanes, other engineeringplastics, and blends of any two or more of the polymers listed herein.

Any of the previously listed crystalline or semi-crystalline polymerparticles may be combined with ceramic particles to form the polymericcomposite build material particles 16. Examples of suitable ceramicparticles include metal oxides, inorganic glasses, carbides, nitrides,and borides. Some specific examples include alumina (Al₂O₃), glass,silicon mononitride (SiN), silicon dioxide (SiO₂), zirconia (ZrO₂),titanium dioxide (TiO₂), or combinations thereof. The amount of ceramicparticles that may be combined with the crystalline or semi-crystallinepolymer particles may depend on the materials used and the final 3Dobject to be formed. In one example, the ceramic particles may bepresent in an amount ranging from about 1 wt % to about 40 wt % based onthe total weight of the polymeric composite build material particles 16.

In some examples, the polymeric or polymeric composite build material 16may be in the form of a powder. In other examples, the build material 16may be in the form of a powder-like material, which includes, forexample, short fibers having a length that is greater than its width. Insome examples, the powder may be formed from, or may include, shortfibers that may, for example, have been cut into short lengths from longstrands or threads of material.

The polymeric or polymeric composite build material particles 16 mayhave a melting point or softening point ranging from about 50° C. toabout 400° C. Depending upon the composition of the composite, themelting or softening point may be higher or lower. As an example, thematerial particles 16 may be a polyamide having a melting point of about180° C.

The polymeric or polymeric composite build material particles 16 may bemade up of similarly sized particles or differently sized particles. Inthe examples shown herein (FIGS. 2A-2E and FIG. 4), the build material16 includes similarly sized particles. In an example, the averageparticle size of the build material particles 16 ranges from about 2 μmto about 200 μm. In another example, the average particle size of thebuild material particles 16 ranges from about 20 μm to about 90 μm. Instill another example, the average particle size of the build materialparticles 16 is about 60 μm.

In some examples, the polymeric or polymeric composite build material 16includes, in addition to the polymer particles (and in some casesceramic particles), an antioxidant, a brightener, a charging agent, aflow aid, or a combination thereof.

Antioxidant(s) may be added to the polymeric or polymeric compositebuild material 16 to prevent or slow molecular weight decreases of thebuild material 16 and/or may prevent or slow discoloration (e.g.,yellowing) of the build material 16 by preventing or slowing oxidationof the build material 16. In some examples, the antioxidant may be aradical scavenger. In these examples, the antioxidant may includeIRGANOX® 1098 (benzenepropanamide,N,N′-1,6-hexanediylbis(3,5-bis(1,1-dimethylethyl)-4-hydroxy)), IRGANOX®254 (a mixture of 40% triethylene glycolbis(3-tert-butyl-4-hydroxy-5-methylphenyl), polyvinyl alcohol anddeionized water), and/or other sterically hindered phenols. In otherexamples, the antioxidant may include a phosphite and/or an organicsulfide (e.g., a thioester). In an example, the antioxidant may beincluded in the polymeric or polymeric composite build material 16 in anamount ranging from about 0.01 wt % to about 5 wt % based on the totalweight of the build material 16.

Brightener(s) may be added to the build material 16 to improvevisibility. Examples of suitable brighteners include titanium dioxide(TiO₂), zinc oxide (ZnO), calcium carbonate (CaCO₃), zirconium dioxide(ZrO₂), aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), and combinationsthereof. In some examples, a stilbene derivative may be used as thebrightener. In these examples, the temperature(s) of the 3D printingprocess may be below a threshold temperature above which the stilbenederivative may become unstable. In an example, the brightener may beincluded in the polymeric or polymeric composite build material 16 in anamount ranging from about 0.01 wt % to about 10 wt % based on the totalweight of the polymeric or polymeric composite build material 16.

Charging agent(s) may be added to the build material 16 to suppresstribo-charging. Examples of suitable charging agents include aliphaticamines (which may be ethoxylated), aliphatic amides, quaternary ammoniumsalts (e.g., behentrimonium chloride or cocamidopropyl betaine), estersof phosphoric acid, polyethylene glycolesters, or polyols. Some suitablecommercially available charging agents include HOSTASTAT® FA 38 (naturalbased ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), andHOSTASTAT® HS 1 (alkane sulfonate), each of which is available fromClariant Int. Ltd.). In an example, the charging agent is added in anamount ranging from greater than 0 wt % to less than 5 wt % based uponthe total weight of the polymeric or polymeric composite build material16.

Flow aid(s) may be added to improve the coating flowability of the buildmaterial 16. Flow aids may be particularly beneficial when the particlesof the build material 16 are less than 25 μm in size. The flow aidimproves the flowability of the polymeric or polymeric composite buildmaterial 16 by reducing the friction, the lateral drag, and thetribocharge buildup (by increasing the particle conductivity). Examplesof suitable flow aids include tricalcium phosphate (E341), powderedcellulose (E460(ii)), magnesium stearate (E470b), sodium bicarbonate(E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536),calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate(E550), silicon dioxide (E551), calcium silicate (E552), magnesiumtrisilicate (E553a), talcum powder (E553b), sodium aluminosilicate(E554), potassium aluminum silicate (E555), calcium aluminosilicate(E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570),or polydimethylsiloxane (E900). In an example, the flow aid is added inan amount ranging from greater than 0 wt % to less than 5 wt % basedupon the total weight of the polymeric or polymeric composite buildmaterial 16.

Also in some examples of the method 100, 200 and the system 10 disclosedherein, and as mentioned above, a fusing agent 26 may be used. Examplesof the fusing agent 26 are dispersions including a radiation absorber(i.e., an active material). The active material may be any infraredlight absorbing colorant. In an example, the active material is anear-infrared light absorber. Any near-infrared colorants, e.g., thoseproduced by Fabricolor, Eastman Kodak, or Yamamoto, may be used in thefusing agent 26. As one example, the fusing agent 26 may be a printingliquid formulation including carbon black as the active material.Examples of this printing liquid formulation are commercially known asCM997A, 516458, C18928, C93848, C93808, or the like, all of which areavailable from HP Inc. Other suitable active materials includenear-infrared absorbing dyes or plasmonic resonance absorbers.

As another example, the fusing agent 26 may be a printing liquidformulation including near-infrared absorbing dyes as the activematerial. Examples of this printing liquid formulation are described inU.S. Pat. No. 9,133,344, incorporated herein by reference in itsentirety. Some examples of the near-infrared absorbing dye are watersoluble near-infrared absorbing dyes selected from the group consistingof:

and mixtures thereof. In the above formulations, M can be a divalentmetal atom (e.g., copper, etc.) or can have OSO₃Na axial groups fillingany unfilled valencies if the metal is more than divalent (e.g., indium,etc.), R can be any C1-C8 alkyl group (including substituted alkyl andunsubstituted alkyl), and Z can be a counterion such that the overallcharge of the near-infrared absorbing dye is neutral. For example, thecounterion can be sodium, lithium, potassium, NH₄ ⁺, etc.

Some other examples of the near-infrared absorbing dye are hydrophobicnear-infrared absorbing dyes selected from the group consisting of:

and mixtures thereof. For the hydrophobic near-infrared absorbing dyes,M can be a divalent metal atom (e.g., copper, etc.) or can include ametal that has Cl, Br, or OR′ (R′═H, CH₃, COCH₃, COCH₂COOCH₃,COCH₂COCH₃) axial groups filling any unfilled valencies if the metal ismore than divalent, and R can be any C1-C8 alkyl group (includingsubstituted alkyl and unsubstituted alkyl).

In other examples, the active material may be a plasmonic resonanceabsorber. The plasmonic resonance absorber allows the fusing agent 26 toabsorb radiation at wavelengths ranging from 800 nm to 4000 nm (e.g., atleast 80% of radiation having wavelengths ranging from 800 nm to 4000 nmis absorbed), which enables the fusing agent 26 to convert enoughradiation to thermal energy so that the polymeric or polymeric compositebuild material particles 16 fuse. The plasmonic resonance absorber alsoallows the fusing agent 26 to have transparency at wavelengths rangingfrom 400 nm to 780 nm (e.g., 20% or less of radiation having wavelengthsranging from 400 nm to 780 nm is absorbed), which enables the final 3Dobject 44 to be white or slightly colored.

The absorption of the plasmonic resonance absorber is the result of theplasmonic resonance effects. Electrons associated with the atoms of theplasmonic resonance absorber may be collectively excited by radiation,which results in collective oscillation of the electrons. Thewavelengths that can excite and oscillate these electrons collectivelyare dependent on the number of electrons present in the plasmonicresonance absorber particles, which in turn is dependent on the size ofthe plasmonic resonance absorber particles. The amount of energy thatcan collectively oscillate the particle's electrons is low enough thatvery small particles (e.g., 1-100 nm) may absorb radiation withwavelengths several times (e.g., from 8 to 800 or more times) the sizeof the particles. The use of these particles allows the fusing agent 26to be inkjet jettable as well as electromagnetically selective (e.g.,having absorption at wavelengths ranging from 800 nm to 4000 nm andtransparency at wavelengths ranging from 400 nm to 780 nm).

In an example, the plasmonic resonance absorber has an average particlediameter (e.g., volume-weighted mean diameter) ranging from greater than0 nm to less than 220 nm. In another example the plasmonic resonanceabsorber has an average particle diameter ranging from greater than 0 nmto 120 nm. In a still another example, the plasmonic resonance absorberhas an average particle diameter ranging from about 10 nm to about 200nm.

In an example, the plasmonic resonance absorber is an inorganic pigment.Examples of suitable inorganic pigments include lanthanum hexaboride(LaB₆), tungsten bronzes (A_(x)WO₃), indium tin oxide (In₂O₃:SnO₂, ITO),aluminum zinc oxide (AZO), ruthenium oxide (RuO₂), silver (Ag), gold(Au), platinum (Pt), iron pyroxenes (A_(x)Fe_(y)Si₂O₆ wherein A is Ca orMg, x=1.5-1.9, and y=0.1-0.5), modified iron phosphates(A_(x)Fe_(y)PO₄), and modified copper pyrophosphates (A_(x)Cu_(y)P₂O₇).Tungsten bronzes may be alkali doped tungsten oxides. Examples ofsuitable alkali dopants (i.e., A in A_(x)WO₃) may be cesium, sodium,potassium, or rubidium. In an example, the alkali doped tungsten oxidemay be doped in an amount ranging from greater than 0 mol % to about0.33 mol % based on the total mol % of the alkali doped tungsten oxide.Suitable modified iron phosphates (A_(x)Fe_(y)PO₄) may include copperiron phosphate (A=Cu, x=0.1-0.5, and y=0.5-0.9), magnesium ironphosphate (A=Mg, x=0.1-0.5, and y=0.5-0.9), and zinc iron phosphate(A=Zn, x=0.1-0.5, and y=0.5-0.9). For the modified iron phosphates, itis to be understood that the number of phosphates may change based onthe charge balance with the cations. Suitable modified copperpyrophosphates (A_(x)Cu_(y)P₂O₇) include iron copper pyrophosphate(A=Fe, x=0-2, and y=0-2), magnesium copper pyrophosphate (A=Mg, x=0-2,and y=0-2), and zinc copper pyrophosphate (A=Zn, x=0-2, and y=0-2).Combinations of the inorganic pigments may also be used.

The amount of the active material that is present in the fusing agent 26ranges from greater than 0 wt % to about 40 wt % based on the totalweight of the fusing agent 26. In other examples, the amount of theactive material in the fusing agent 26 ranges from about 0.3 wt % to 30wt %, from about 1 wt % to about 20 wt %, from about 1.0 wt % up toabout 10.0 wt %, or from greater than 4.0 wt % up to about 15.0 wt %. Itis believed that these active material loadings provide a balancebetween the fusing agent 26 having jetting reliability and heat and/orelectromagnetic radiation absorbance efficiency.

As used herein, “FA vehicle” may refer to the liquid in which the activematerial is dispersed or dissolved to form the fusing agent 26. A widevariety of FA vehicles, including aqueous and non-aqueous vehicles, maybe used in the fusing agent 26. In some examples, the FA vehicle mayinclude water alone or a non-aqueous solvent alone with no othercomponents. In other examples, the FA vehicle may include othercomponents, depending, in part, upon the first applicator 24A that is tobe used to dispense the fusing agent 26. Examples of other suitablefusing agent components include dispersant(s), silane coupling agent(s),co-solvent(s), surfactant(s), antimicrobial agent(s), anti-kogationagent(s), and/or chelating agent(s).

When the active material is the plasmonic resonance absorber, theplasmonic resonance absorber may, in some instances, be dispersed with adispersant. As such, the dispersant helps to uniformly distribute theplasmonic resonance absorber throughout the fusing agent 26. Examples ofsuitable dispersants include polymer or small molecule dispersants,charged groups attached to the plasmonic resonance absorber surface, orother suitable dispersants. Some specific examples of suitabledispersants include a water soluble acrylic acid polymer (e.g.,CARBOSPERSE® K7028 available from Lubrizol), water-solublestyrene-acrylic acid copolymers/resins (e.g., JONCRYL® 296, JONCRYL®671, JONCRYL® 678, JONCRYL® 680, JONCRYL® 683, JONCRYL® 690, etc.available from BASF Corp.), a high molecular weight block copolymer withpigment affinic groups (e.g., DISPERBYK®-190 available BYK Additives andInstruments), or water-soluble styrene-maleic anhydridecopolymers/resins.

Whether a single dispersant is used or a combination of dispersants isused, the total amount of dispersant(s) in the fusing agent 26 may rangefrom about 10 wt % to about 200 wt % based on the weight of theplasmonic resonance absorber in the fusing agent 26.

When the active material is the plasmonic resonance absorber, a silanecoupling agent may also be added to the fusing agent 26 to help bond theorganic and inorganic materials. Examples of suitable silane couplingagents include the SILQUEST® A series manufactured by Momentive.

Whether a single silane coupling agent is used or a combination ofsilane coupling agents is used, the total amount of silane couplingagent(s) in the fusing agent 26 may range from about 0.1 wt % to about50 wt % based on the weight of the plasmonic resonance absorber in thefusing agent 26. In an example, the total amount of silane couplingagent(s) in the fusing agent 26 ranges from about 1 wt % to about 30 wt% based on the weight of the plasmonic resonance absorber. In anotherexample, the total amount of silane coupling agent(s) in the fusingagent 26 ranges from about 2.5 wt % to about 25 wt % based on the weightof the plasmonic resonance absorber.

The solvent of the fusing agent 26 may be water or a non-aqueous solvent(e.g., ethanol, acetone, n-methyl pyrrolidone, aliphatic hydrocarbons,etc.). In some examples, the fusing agent 26 consists of the activematerial and the solvent (without other components). In these examples,the solvent makes up the balance of the fusing agent 26.

The co-solvent(s) that may be used in a water-based fusing agent 26include any of the co-solvents listed above in reference to theanti-coalescing agent 28. The co-solvent(s) may be present in the fusingagent 26 in a total amount ranging from about 1 wt % to about 50 wt %based upon the total weight of the fusing agent 26, depending upon thejetting architecture of the applicator 24. In an example, the totalamount of the co-solvent(s) present in the fusing agent 26 is 25 wt %based on the total weight of the fusing agent 26.

Similar to the anti-coalescing agent 28, the co-solvent(s) of the fusingagent 26 may depend, in part upon the jetting technology that is to beused to dispense the fusing agent 26. For example, if thermal inkjetprintheads are to be used, water and/or ethanol and/or other longerchain alcohols (e.g., pentanol) may be the solvent (i.e., makes up 35 wt% or more of the fusing agent 26) or co-solvents. For another example,if piezoelectric inkjet printheads are to be used, water may make upfrom about 25 wt % to about 30 wt % of the fusing agent 26, and thesolvent (i.e., 35 wt % or more of the fusing agent 26) may be ethanol,isopropanol, acetone, etc.

In some examples, the FA vehicle includes surfactant(s) to improve thejettability of the fusing agent 26. Examples of suitable surfactantsinclude the surfactants listed above in reference to the anti-coalescingagent 28. Whether a single surfactant is used or a combination ofsurfactants is used, the total amount of surfactant(s) in the fusingagent 26 may range from about 0.01 wt % to about 10 wt % based on thetotal weight of the fusing agent 26. In an example, the total amount ofsurfactant(s) in the fusing agent 26 may be about 3 wt % based on thetotal weight of the fusing agent 26.

An anti-kogation agent may be included in the fusing agent 26 that is tobe jetted using thermal inkjet printing. Kogation refers to the depositof dried printing liquid (e.g., fusing agent 26) on a heating element ofa thermal inkjet printhead. Anti-kogation agent(s) is/are included toassist in preventing the buildup of kogation. Examples of suitableanti-kogation agents include oleth-3-phosphate (e.g., commerciallyavailable as CRODAFOS™ O3A or CRODAFOS™ N-3 acid from Croda), or acombination of oleth-3-phosphate and a low molecular weight (e.g.,<5,000) polyacrylic acid polymer (e.g., commercially available asCARBOSPERSE™ K-7028 Polyacrylate from Lubrizol).

Whether a single anti-kogation agent is used or a combination ofanti-kogation agents is used, the total amount of anti-kogation agent(s)in the fusing agent 26 may range from greater than 0.20 wt % to about0.65 wt % based on the total weight of the fusing agent 26. In anexample, the oleth-3-phosphate is included in an amount ranging fromabout 0.20 wt % to about 0.60 wt %, and the low molecular weightpolyacrylic acid polymer is included in an amount ranging from about0.005 wt % to about 0.03 wt %.

The FA vehicle may also include antimicrobial agent(s). Suitableantimicrobial agents include biocides and fungicides. Exampleantimicrobial agents may include the NUOSEPT™ (Troy Corp.), UCARCIDE™(Dow Chemical Co.), ACTICIDE® B20 (Thor Chemicals), ACTICIDE® M20 (ThorChemicals), ACTICIDE® MBL (blends of 2-methyl-4-isothiazolin-3-one(MIT), 1,2-benzisothiazolin-3-one (BIT) and Bronopol) (Thor Chemicals),AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under thetradename KATHON™ (Dow Chemical Co.), and combinations thereof. Examplesof suitable biocides include an aqueous solution of1,2-benzisothiazolin-3-one (e.g., PROXEL® GXL from Arch Chemicals,Inc.), quaternary ammonium compounds (e.g., BARDAC® 2250 and 2280,BARQUAT® 50-65B, and CARBOQUAT® 250-T, all from Lonza Ltd. Corp.), andan aqueous solution of methylisothiazolone (e.g., KORDEK® MLX from DowChemical Co.).

In an example, the fusing agent 26 may include a total amount ofantimicrobial agents that ranges from about 0.05 wt % to about 1 wt %.In an example, the antimicrobial agent(s) is/are a biocide(s) and is/arepresent in the fusing agent 26 in an amount of about 0.25 wt % (based onthe total weight of the fusing agent 26).

Chelating agents (or sequestering agents) may be included in the FAvehicle to eliminate the deleterious effects of heavy metal impurities.Examples of chelating agents include disodium ethylenediaminetetraaceticacid (EDTA-Na), ethylene diamine tetra acetic acid (EDTA), andmethylglycinediacetic acid (e.g., TRILON® M from BASF Corp.).

Whether a single chelating agent is used or a combination of chelatingagents is used, the total amount of chelating agent(s) in the fusingagent 26 may range from greater than 0 wt % to about 2 wt % based on thetotal weight of the fusing agent 26. In an example, the chelatingagent(s) is/are present in the fusing agent 26 in an amount of about0.04 wt % (based on the total weight of the fusing agent 26).

Also in some examples of the method 100, 200 and the system 10 disclosedherein, and as mentioned above, the detailing agent 52 may be used. Thedetailing agent 52 may include a surfactant, a co-solvent, and a balanceof water. In some examples, the detailing agent 52 consists of thesecomponents, and no other components. In some other examples, thedetailing agent 52 may further include a colorant. In still some otherexamples, detailing agent 52 consists of a colorant, a surfactant, aco-solvent, and a balance of water, with no other components. In yetsome other examples, the detailing agent 52 may further includeadditional components, such as anti-kogation agent(s), antimicrobialagent(s), and/or chelating agent(s) (each of which is described above inreference to the fusing agent 26).

The surfactant(s) that may be used in the detailing agent 52 include anyof the surfactants listed above in reference to the anti-coalescingagent 28. The total amount of surfactant(s) in the detailing agent 52may range from about 0.10 wt % to about 5.00 wt % with respect to thetotal weight of the detailing agent 52.

The co-solvent(s) that may be used in the detailing agent 52 include anyof the co-solvents listed above in reference to the anti-coalescingagent 28. The total amount of co-solvent(s) in the detailing agent 52may range from about 1.00 wt % to about 20.00 wt % with respect to thetotal weight of the detailing agent 52.

Similar to the anti-coalescing agent 28 and the fusing agent 26, theco-solvent(s) of the detailing agent 52 may depend, in part upon thejetting technology that is to be used to dispense the detailing agent52. For example, if thermal inkjet printheads are to be used, waterand/or ethanol and/or other longer chain alcohols (e.g., pentanol) maymake up 35 wt % or more of the detailing agent 52. For another example,if piezoelectric inkjet printheads are to be used, water may make upfrom about 25 wt % to about 30 wt % of the detailing agent 52, and 35 wt% or more of the detailing agent 52 may be ethanol, isopropanol,acetone, etc.

When the detailing agent 52 includes the colorant, the colorant may be adye of any color having substantially no absorbance in a range of 650 nmto 2500 nm. By “substantially no absorbance” it is meant that the dyeabsorbs no radiation having wavelengths in a range of 650 nm to 2500 nm,or that the dye absorbs less than 10% of radiation having wavelengths ina range of 650 nm to 2500 nm. The dye is also capable of absorbingradiation with wavelengths of 650 nm or less. As such, the dye absorbsat least some wavelengths within the visible spectrum, but absorbslittle or no wavelengths within the near-infrared spectrum. This is incontrast to the active material in the fusing agent 26, which absorbswavelengths within the near-infrared spectrum. As such, the colorant inthe detailing agent 52 will not substantially absorb the fusingradiation, and thus will not initiate melting and fusing of thepolymeric or polymeric composite build material 16 in contact therewithwhen the layer 40 is exposed to the fusing radiation.

The dye selected as the colorant in the detailing agent 52 may also havea high diffusivity (i.e., it may penetrate into greater than 10 μm andup to 100 μm of the build material particles 16). The high diffusivityenables the dye to penetrate into the build material particles 16 uponwhich the detailing agent 52 is applied, and also enables the dye tospread into portions of the build material 16 that are adjacent to theportions of the build material 16 upon which the detailing agent 52 isapplied. The dye penetrates deep into the build material particles 16 todye/color the particles 16. When the detailing agent 52 is applied at orjust outside the edge boundary 33 (of the final 3D object 44), the buildmaterial particles 16 at the edge boundary 33 may be colored. In someexamples, at least some of these dyed build material particles 16 may bepresent at the edge(s) or surface(s) of the formed 3D layer or object,which prevents or reduces any patterns (due to the different colors ofthe fusing agent 26 and the polymeric or polymeric composite buildmaterial 16) from forming at the edge(s) or surface(s).

The dye in the detailing agent 52 may be selected so that its colormatches the color of the active material in the fusing agent 26. Asexamples, the dye may be any azo dye having sodium or potassium counterion(s) or any diazo (i.e., double azo) dye having sodium or potassiumcounter ion(s), where the color of azo or dye azo dye matches the colorof the fusing agent 26.

In an example, the dye is a black dye. Some examples of the black dyeinclude azo dyes having sodium or potassium counter ion(s) and diazo(i.e., double azo) dyes having sodium or potassium counter ion(s).Examples of azo and diazo dyes may include tetrasodium(6Z)-4-acetamido-5-oxo-6-[[7-sulfonato-4-(4-sulfonatophenyl)azo-1-naphthyl]hydrazono]naphthalene-1,7-disulfonatewith a chemical structure of:

(commercially available as Food Black 1); tetrasodium6-amino-4-hydroxy-3-[[7-sulfonato-4-[(4-sulfonatophenyl)azo]-1-naphthyl]azo]naphthalene-2,7-disulfonatewith a chemical structure of:

(commercially available as Food Black 2); tetrasodium(6E)-4-amino-5-oxo-3-[[4-(2-sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2-sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene-2,7-disulfonatewith a chemical structure of:

(commercially available as Reactive Black 31); tetrasodium(6E)-4-amino-5-oxo-3-[[4-(2-sulfonatooxyethylsulfonyl)phenyl]diazenyl]-6-[[4-(2-sulfonatooxyethylsulfonyl)phenyl]hydrazinylidene]naphthalene-2,7-disulfonatewith a chemical structure of:

and combinations thereof. Some other commercially available examples ofthe dye used in the detailing agent 52 include multipurpose blackazo-dye based liquids, such as PRO-JET® Fast Black 1 (made available byFujifilm Holdings), and black azo-dye based liquids with enhanced waterfastness, such as PRO-JET® Fast Black 2 (made available by FujifilmHoldings).

In some instances, in addition to the black dye, the colorant in thedetailing agent 52 may further include another dye. In an example, theother dye may be a cyan dye that is used in combination with any of thedyes disclosed herein. The other dye may also have substantially noabsorbance above 650 nm. The other dye may be any colored dye thatcontributes to improving the hue and color uniformity of the final 3Dobject.

Some examples of the other dye include a salt, such as a sodium salt, anammonium salt, or a potassium salt. Some specific examples includeethyl-[4-[[4-[ethyl-[(3-sulfophenyl) methyl] amino]phenyl]-(2-sulfophenyl)ethylidene]-1-cyclohexa-2,5-dienylidene]-[(3-sulfophenyl) methyl]azanium with a chemical structure of:

(commercially available as Acid Blue 9, where the counter ion mayalternatively be sodium counter ions or potassium counter ions); sodium4-[(E)-{4-[benzyl(ethyl)amino]phenyl}{(4E)-4-[benzyl(ethyl)iminio]cyclohexa-2,5-dien-1-ylidene}methyl]benzene-1,3-disulfonatewith a chemical structure of:

(commercially available as Acid Blue 7); and a phthalocyanine with achemical structure of:

(commercially available as Direct Blue 199); and combinations thereof.

In an example of the detailing agent 52, the dye may be present in anamount ranging from about 1.00 wt % to about 3.00 wt % based on thetotal weight of the detailing agent 52. In another example of thedetailing agent 52 including a combination of dyes, one dye (e.g., theblack dye) is present in an amount ranging from about 1.50 wt % to about1.75 wt % based on the total weight of the detailing agent 52, and theother dye (e.g., the cyan dye) is present in an amount ranging fromabout 0.25 wt % to about 0.50 wt % based on the total weight of thedetailing agent 52.

The balance of the detailing agent 52 is water. As such, the amount ofwater may vary depending upon the amounts of the other components thatare included.

To further illustrate the present disclosure, examples are given herein.It is to be understood these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

EXAMPLES Example 1

Examples of the anti-coalescing agent (ACA) were prepared. The exampleanti-coalescing agents included perfluoroalkoxy alkane,poly(tetrafluoroethylene), or perfluorinated polyether as theanti-coalescing polymer. The general formulations of the exampleanti-coalescing agents are shown below in Table 1, with the wt % of eachcomponent that was used.

TABLE 1 E.g. E.g. E.g. ACA 1 ACA 2 ACA 3 Ingredient Specific component(wt %) (wt %) (wt %) Anti- Perfluoroalkoxy alkane 3-10 — — coalescingPoly(tetrafluoroethylene) — 3-10 — polymer Perfluorinated polyether — —3-10 Co-solvent 2-pyrrolidone 5-15 5-15 5-15 Triethylene glycol 5-105-10 5-10 Surfactant TERGITOL ™ TMN-6 0.5-1   0.5-1   0.5-1   TERGITOL ™15-S-30 0.25-1    0.25-1    0.25-1    TEGO ® Wet 510 0.25-1    0.25-1   0.25-1    DOWFAX ™ 2A1 0.1-1   0.1-1   0.1-1   Humectant LIPONIC ® EG-13-8  3-8  3-8  Water Deionized water Balance Balance Balance

The formulations for the example anti-coalescing agents in Table 1 aresuitable for being printed via thermal inkjet printheads. It is believedthat formulations for piezoelectric printheads may include differentamounts and/or different components.

Example 2

Six tin pans of polyamide 12 (PA 12) powder were prepared.Perfluoroalkoxy alkane (dispersed in water), an example anti-coalescingpolymer, was applied on a portion of the polyamide 12 powder in thefirst tin pan. Poly(tetrafluoroethylene) (dispersed in water), anotherexample anti-coalescing polymer, was applied on a portion of thepolyamide 12 powder in the second tin pan. One of the exampleanti-coalescing agents, e.g. ACA 1, was applied on a portion of thepolyamide 12 powder in the third tin pan.

Polyethylene wax (LIQUILUBE™ 405 available from Lubrizol Corp.), acomparative anti-coalescing polymer, was applied on a portion of thepolyamide 12 powder in the fourth tin pan. Tetrafluoroethylenehexafluoropropylene vinylidene fluoride (dispersed in water), anothercomparative anti-coalescing polymer, was applied on a portion of thepolyamide 12 powder in the fifth tin pan. The sixth tin pan of polyamide12 powder was not treated.

Each of the tin pans was heated in an oven to about 200° C. (i.e., about15° C. above the melting temperature of polyamide 12 powder). After 1hour in the oven at 200° C., the non-treated polyamide 12 powder in eachof the six tin pans was melted. After 1 hour in the oven at 200° C., theportions of the polyamide 12 powder treated with the comparativeanti-coalescing polymers also melted. In contrast, after 1 hour in theoven at 200° C., the portions of the polyamide 12 powder treated withthe example anti-coalescing polymers were each a cake of powder that waseasily broken apart and removed from the melted portions.

Example 3

One of the example anti-coalescing agents from Example 1, e.g. ACA 1,was mixed with polyamide 12 powder at a weight ratio of 1:1. An about200 μm thick layer of the mixture was deposited on a glass slide to forman example removable build material portion. An about 200 μm thick layerof the polyamide 12 powder alone (i.e., without any liquids or agents)was deposited on anther glass slide to form a comparative portion. Eachglass slide with the layer thereon was heated to 210° C. on a stage thatenabled controlled heating of the layers and observation of the layersunder a microscope.

FIG. 5A shows the comparative portion, at 100 times magnification,before it was heated to 210° C., and FIG. 5B shows the comparativeportion, at 100 times magnification, after it was heated to 210° C. Asshown in FIG. 5B, the comparative portion melted/coalesced to form apolymer film. FIG. 5C shows the example removable build materialportion, at 100 times magnification, before it was heated to 210° C.,and FIG. 5D shows the example removable build material portion, at 100times magnification, after it was heated to 210° C. As shown in FIG. 5D,the powder particles in the example removable build material portionremained distinct particles and did not coalesce. As also shown in FIG.5D, the powder particles appeared to become more translucent.

Example 4

One of the example anti-coalescing agents from Example 1, e.g. ACA 1,was used to print three example 3D objects. The build material waspolyamide 12 powder, and the fusing agent included carbon black as theactive material.

In each layer of the first example 3D object, the fusing agent wasapplied on a solid rectangle of the build material powder. Then, theexample anti-coalescing agent was applied in a pattern to form a seriesof 1 cm by 2 mm strips along one side of the rectangle (to which thefusing agent was applied). A comparative anti-coalescing agent, havingthe same formulation as the example anti-coalescing agent except thatthe comparative anti-coalescing agent did not include an anti-coalescingpolymer, was applied in a pattern to form another series of 1 cm by 2 mmstrips along the other side of the rectangle (to which the fusing agentwas applied). On each side of the rectangle, the agent was applied inthe first strip in an amount of 5 g/m², in the second strip in an amountof 10 g/m², in the third strip in an amount of 15 g/m², in the fourthstrip in an amount of 20 g/m², in the fifth strip in an amount of 25g/m², in the sixth strip in an amount of 30 g/m², in the seventh stripin an amount of 35 g/m², and in the eighth strip in an amount of 40g/m². Then, radiation was applied to fuse each layer.

The comparative anti-coalescing agent did affect the coalescence of thebuild material powder, but the same amount of the exampleanti-coalescing agent improved the prevention of the coalescence of thebuild material powder (as compared to the prevention of the coalescenceof the build material powder achieved with the same amount of thecomparative anti-coalescing agent). All of the strips, to which thecomparative anti-coalescing agent was applied, at least partiallycoalesced. In contrast, the eighth strip, to which 40 g/m² of theexample anti-coalescing agent was applied, did not coalesce, and almostall of the seventh strip, to which 35 g/m² of the exampleanti-coalescing agent was applied, did not coalesce.

In each layer of the second example 3D object, the fusing agent wasapplied on a solid rectangle of the build material powder. Then, theexample anti-coalescing agent was applied in a pattern to form in eightcylinders with a 1 mm diameter and eight cylinders with a 2 mm diameterwithin the rectangle (to which the fusing agent was applied). Theexample anti-coalescing agent was applied to the first two 1 mm diametercylinders and the first two 2 mm diameter cylinders in an amount of 10g/m², to the second two 1 mm diameter cylinders and the second two 2 mmdiameter cylinders in an amount of 20 g/m², to the third two 1 mmdiameter cylinders and the third two 2 mm diameter cylinders in anamount of 30 g/m², and to the fourth two 1 mm diameter cylinders and thefourth two 2 mm diameter cylinders in an amount of 40 g/m². Then,radiation was applied to fuse each layer.

A comparative 3D object was printed in the same way, except that thecomparative anti-coalescing agent (having the same formulation as theexample anti-coalescing agent except that the comparativeanti-coalescing agent did not include an anti-coalescing polymer), andnot the example anti-coalescing agent, was applied in the pattern toform the eight cylinders with a 1 mm diameter and the eight cylinderswith a 2 mm diameter within the rectangle (to which the fusing agent wasapplied). The amounts of comparative anti-coalescing agent applied tothe cylinders in the comparative 3D object were the same as the amountsof example anti-coalescing agent applied to the cylinders in the secondexample 3D object.

FIG. 6A shows the second example 3D object after standard postprocessing, and FIG. 6B shows the comparative 3D object after standardpost processing. Standard post processing for each of the second example3D object and the comparative 3D object included bead blasting. As shownin FIGS. 6A and 6B, the example anti-coalescing agent improved theprevention of the coalescence of the build material powder (as comparedto the prevention of the coalescence of the build material powderachieved with the same amount of the comparative anti-coalescing agent).

None of the cylinders, to which the comparative anti-coalescing agentwas applied, were able to be even partially cleared. Further, applyingthe comparative anti-coalescing agent at 40 g/m² resulted in a similardegree of fusion as applying the comparative anti-coalescing agent at 10g/m².

In contrast, both of the 2 mm diameter cylinders, to which 40 g/m² ofthe example anti-coalescing agent was applied, were able to be cleared,and both of the 2 mm diameter cylinders, to which 30 g/m² of the exampleanti-coalescing agent was applied, had a low degree of fusion and wereable to be partially cleared. While the 1 mm diameter cylinders were notable to be cleared, it is believed that if the fusing agent was notapplied or if less of the fusing agent was applied to the 1 mm diametercylinders, the example anti-coalescing agent may have been able toprevent the coalescence of the build material powder within the 1 mmdiameter cylinders such that they could have been cleared.

The third example 3D object was printed to form a plate with ten sets oftwo vertical titles separated by a small gap (i.e., ten gaps werecreated). The first two gaps had a thickness of 0.1 mm, the second twogaps had a thickness of 0.2 mm, the third two gaps had a thickness of0.3 mm, the fourth two gaps had a thickness of 0.4 mm, and the fifth twogaps had a thickness of 0.5 mm. The example anti-coalescing agent wasapplied in one gap of each thickness, and the comparativeanti-coalescing agent (having the same formulation as the exampleanti-coalescing agent except that the comparative anti-coalescing agentdid not include an anti-coalescing polymer) was applied in the other gapof each thickness. The third example 3D object was printed several timesin each of a default orientation and an orientation rotated 180 degreesfrom the default orientation so that results were not affected by anytemperature non-uniformity in the printbed.

The example anti-coalescing agent improved the prevention of thecoalescence of the build material powder (as compared to the preventionof the coalescence of the build material powder achieved with the sameamount of the comparative anti-coalescing agent). The comparativeanti-coalescing agent was able to reliably clear the 0.5 mm gap suchthat the vertical titles could be separated after printing and was ableto intermittently clear the 0.4 mm gap depending on the location of the0.4 mm gap in the printbed. In contrast, the example anti-coalescingagent was able to reliably clear the 0.3 mm gap regardless of thelocation of the 0.3 mm gap in the printbed.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, from about 3 wt % to about 10 wt % should be interpreted toinclude not only the explicitly recited limits of from about 3 wt % toabout 10 wt %, but also to include individual values, such as about 4 wt%, about 5.1 wt %, about 7.25 wt %, about 8.85 wt %, about 9.5 wt %,etc., and sub-ranges, such as from about 3.5 wt % to about 7.35 wt %,from about 3.15 wt % to about 9.5 wt %, from about 5 wt % to about 8.5wt %, etc. Furthermore, when “about” is utilized to describe a value,this is meant to encompass minor variations (up to +/−10%) from thestated value.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. An anti-coalescing agent for a three-dimensional(3D) printing process, comprising: a vehicle, comprising: a co-solvent;a surfactant; a humectant; and water; and an anti-coalescing polymerdispersed in the vehicle, the anti-coalescing polymer having a meanparticle size ranging from about 50 nm to about 195 nm, and theanti-coalescing polymer to coat polymeric build material particles toprevent the polymeric build material particles from coalescing duringelectromagnetic radiation exposure of the 3D printing process.
 2. Theanti-coalescing agent as defined in claim 1 wherein the anti-coalescingpolymer is a perfluorinated polymer.
 3. The anti-coalescing agent asdefined in claim 2 wherein the perfluorinated polymer is selected fromthe group consisting of a perfluoroalkoxy alkane,poly(tetrafluoroethylene), a perfluorinated polyether, fluorinatedethylene propylene, and combinations thereof.
 4. The anti-coalescingagent as defined in claim 1 wherein the anti-coalescing agent has asurface tension ranging from about 20 dynes/cm to about 28 dynes/cm. 5.The anti-coalescing agent as defined in claim 1, wherein the surfactantcomprises: a first non-ionic surfactant having a first hydrophilic chainlength; a second non-ionic surfactant having a second hydrophilic chainlength that is different than the first hydrophilic chain length; athird non-ionic surfactant, wherein the third non-ionic surfactant isselected from the group consisting of a polyether siloxane and analkoxylated alcohol; and an anionic surfactant.
 6. A method forthree-dimensional (3D) printing, comprising: applying a polymeric orpolymeric composite build material; negatively patterning some of thepolymeric or polymeric composite build material to define a removablebuild material portion and a remaining build material portion, thenegatively patterning including selectively applying an anti-coalescingagent comprising: a vehicle, comprising: a co-solvent; a surfactant; ahumectant; and water; and an anti-coalescing polymer dispersed in thevehicle, the anti-coalescing polymer having a mean particle size rangingfrom about 50 nm to about 195 nm; and based on a 3D object model,forming a layer of a final 3D object from at least some of the remainingbuild material portion, wherein the some of the polymeric or polymericcomposite build material in the removable build material portion remainsnon-coalesced.
 7. The method as defined in claim 6 wherein theanti-coalescing polymer is a perfluorinated polymer selected from thegroup consisting of a perfluoroalkoxy alkane, poly(tetrafluoroethylene),a perfluorinated polyether, fluorinated ethylene propylene, andcombinations thereof.
 8. The method as defined in claim 6 wherein theforming of the layer involves: based on the 3D object model, selectivelyapplying a fusing agent on the at least some of the remaining buildmaterial portion; and exposing the polymeric or polymeric compositebuild material to radiation to fuse the at least some of the remainingbuild material portion.
 9. The method as defined in claim 8, furthercomprising selectively applying a detailing agent on the at least someof the remaining build material portion to control a fusing temperaturein the remaining build material portion, wherein the detailing agentincludes a surfactant, a co-solvent, and water.
 10. The method asdefined in claim 6 wherein the forming of the layer involves selectivelylaser sintering, based on the 3D object model, the at least some of theremaining build material portion.
 11. The method as defined in claim 6,further comprising selectively applying a detailing agent on the some ofthe polymeric or polymeric composite build material to at leastpartially facilitate wetting of the anti-coalescing agent on the some ofthe polymeric or polymeric composite build material, wherein thedetailing agent includes a surfactant, a co-solvent, and water.
 12. Themethod as defined in claim 6, further comprising selectively applying adetailing agent on a third portion of the polymeric or polymericcomposite build material to prevent the polymeric or polymeric compositebuild material in the third portion from fusing, wherein the thirdportion does not include the removable build material portion or the atleast some of the remaining build material portion, and the detailingagent includes a surfactant, a co-solvent, and water.
 13. The method asdefined in claim 6 wherein the removable build material portion islocated outside of an edge of the remaining build material portion or isat least partially surrounded by the remaining build material portion.14. A three-dimensional (3D) printed article, comprising: a fusedpolymer or polymer composite object; and a removable object in contactwith at least a portion of the fused polymer or polymer compositeobject, the removable object comprising: polymeric or polymericcomposite build material particles; and a polymeric coating formed onsurfaces of the polymeric or polymeric composite build materialparticles and present in voids between the polymeric or polymericcomposite build material particles, wherein the polymeric coating is aperfluorinated polymer.
 15. The 3D printed article as defined in claim14 wherein the perfluorinated polymer is selected from the groupconsisting of a perfluoroalkoxy alkane, poly(tetrafluoroethylene), aperfluorinated polyether, fluorinated ethylene propylene, andcombinations thereof.